Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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PIVOTAL AND VERTICALLY TRANSLATABLE DOCK LEVELER LIP
Background of the Invention
Field of the Invention
The subject invention generally pertains to dock levelers and more
specifically
to a reduced-stress connection between a hinge and a lip of a dock leveler.
Description of Related Art
A typical truck loading dock of a building includes an exterior doorway with
an elevated platform for loading and unloading vehicles such as trucks and
trailers. Many
loading docks have a dock leveler to compensate for a height difference that
may exist
between the floor of the loading dock platform and an adjacent bed of a truck
or trailer. A
typical dock leveler includes a deck that is hinged along its back edge at or
near the elevation
of the floor so that the deck can pivotally adjust the height of its front
edge to an elevation
that generally matches the height of the rear edge of the truck bed to provide
a ramp for
material handling equipment.
In addition, a front hinge may pivotally connect an extension plate or lip to
the
front edge of the deck. The front hinge allows the lip to pivot between a
stored, pendant
position and an extended, operative position. In the extended position, the
lip can rest upon
the truck bed to form a bridge between the deck and the bed. This allows
personnel and
material handling equipment, such as a forklift truck, to readily move on and
off the truck
during loading and unloading operations.
With some dock levelers, the lip is connected to the deck in such a way that
the lip can be used as a barrier to help prevent material handling equipment
from accidentally
driving off the edge of the deck while the deck is in its stored, cross-
traffic position and no
truck is parked at the dock. An example of such a dock leveler is disclosed in
U. S. Patent
4,920,598. With the '598 dock leveler, the lip includes a series of slots
through which a
corresponding series of bolts extend to fasten the lip to a deck hinge. The
slots plus clearance
between the underside of the lip and the hinge allow the lip to slide between
a normal
operating position and a raised barrier position.
When the lip is in its normal operating position and is extended to rest atop
the
back edge of a truck bed, tremendous stress can develop between the lip and
the heads of the
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bolts that fasten the lip to the hinge when loads move over the dock leveler.
The stress is
concentrated along just a portion of the bolt head because the clearance
between the lip and
the hinge allow the lip to cock at a slight angle relative to the contact face
of the bolt head.
With the design disclosed in the '598 patent, the resulting stress
concentrations require the
use of heavier and/or stronger materials than would otherwise be needed.
Summary of the Invention
In some embodiments, a dock leveler includes a lip that not only pivots
between an extended, operative position and a pendant position relative to a
deck but also
translates from a non-blocking pendant position to a blocking pendant
position. A fastener
connects the lip to a hinge in such a way as to minimize the stress between
the fastener and
the lip.
In some embodiments, the hinge includes a lip-facing surface into which the
fastener is anchored, wherein the fastener is tilted out of perpendicularity
to the lip-facing
surface.
In some embodiments, the head of the fastener is held parallel to the lip even
though an angled gap may exist between the lip and the lip-facing surface of
the hinge.
Brief Description of the Drawings
Figure 1 is a side view of a truck backing into a loading dock, wherein the
dock includes a dock leveler whose lip is in a blocking pendant position.
Figure 2 is side view similar to Figure 1 but showing the dock leveler's deck
rising and the lip extending.
Figure 3 is a side view similar to Figures 1 and 2 but showing the deck having
lowered the lip upon the bed of the truck, wherein the lip is at an extended
operative position.
Figure 4 is a side view of the dock leveler in a below-dock end-loading
position with the lip at a non-blocking pendant position.
Figure S is a cross-sectional side view taken along a centerline of a slot
that is
in the dock leveler lip while the lip is in the extended operative position.
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Figure 6 is a cross-sectional view similar to Figure 5 but showing the lip in
its
blocking pendant position.
Figure 7 is a front view of Figure 6 but with a portion of the lip cut away.
Figure 8 is an enlarged cross-sectional view similar to Figure 5.
Figure 9 shows the head-to-lip contact area of a prior art design.
Figure 10 is similar to Figure 9 but showing a more broadly distributed head-
to-lip contact area of the current design.
Figure 11 is a cross-sectional view similar to Figure 5 but showing another
embodiment of the dock leveler.
Figure 12 is a cross-sectional view similar to Figure 6 but showing the lip of
the dock leveler of Figure 11 in a blocking pendant position.
Figure 13 is a front view of Figure 12 but showing a portion of the lip cut
away.
Description of the Preferred Embodiment
Referring to Figures 1 - 8, in order to compensate for a height differential
that
may exist between a loading dock platform 10 and the bed of a truck 12, a dock
leveler 14
includes a ramp or deck 16 that can pivot about its back edge 18 to adjust the
height of its
front edge 20. To bridge the gap between the deck's front edge 20 and the rear
edge of truck
12, a front hinge 22 pivotally connects a lip 24 to the deck's front edge 20.
Deck 16 is
movable to a cross-traffic position (Fig. 1), a raised position (Fig. 2), an
operative position
(Fig. 3), and a below-dock end-loading position (Fig. 4). Lip 24 can pivot
between a pendant
position (Fig. 4) and an extended operative position. Lip 24 can also
translate between a
blocking position (Fig. 1) and the non-blocking pendant position (Fig. 4).
In operation, truck 12 backs into the loading dock, adjacent to platform 10,
as
shown in Figure 1. At this point, deck 16 is at its stored, cross-traffic
position where a
driveway surface 26 of deck 16 is generally flush with the floor of platform
10, and a tip 28
of lip 24 rests upon a set of lip keepers 30, thereby supporting the deck to
allow incidental
traffic across the deck. To prevent items such as a forklift and other
material handling
equipment from accidentally falling over the deck's front edge 20, a back edge
32 of lip 24
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' protnides above the deck's driveway surface 26 to create a barner. This is
accomplished by
providing hinge 22 and lip 24 with a sliding connection 34 between the two,
which will be
explained later.
Next, in Figure 2, deck 16 rises and lip 24 swings out to extend the tip 28 of
lip 24 out over the top of the truck bed. The movement of lip 24 and deck 16
can be carried
out in any of a wide variety of ways that are well known to those of ordinary
skill in the art.
The movement, for example, can be powered, manually driven, or a combination
of the two.
Mechanisms for moving deck 16 or lip 24 include, but are not limited to,
hydraulic cylinder
or bladder, pneumatic cylinder or bladder, mechanical linkage, drive screw,
rack and pinion,
winch, mechanical spring, gas spring, and various combinations thereof.
Regardless of how
deck 16 and lip 24 are moved, prior to extending the lip, deck 16 lifts lip 24
off keepers 30
where the sliding connection between hinge 22 and lip 24 allows the lip's
weight to urge the
lip's back edge 32 downward to where edge 32 is below the deck's driveway
surface 16,
Then, in Figure 3, deck 16 descends to place the extended lip 24 upon the bed
of truck 12. Dock leveler 14 is now in its operative position where truck 12
can be loaded or
unloaded of its cargo. In the operative position, it should be noted that lip
24 and the deck's
traffic surface 26 create a crown 36 having a defining angle 38 of about S-
degrees. Crown 36
ensures that the lip's tip 28 engages the bed of truck 12 even when the truck
bed is higher
than dock platform 10.
Figure 4 illustrates an end-loading position where the non-blocking pendant
lip is lowered in front of and below lip keeper's 30. With lip 24 not resting
atop the truck
bed, loads can be added and removed from the very back end of the truck
without
interference from lip 24.
The sliding connection between lip 24 and hinge 22 can be as described in U.
S. Patent 4,920,598, which is specifically incorporated by reference herein;
however, an
improved, reduced stress sliding connection 34 is illustrated in Figures 5 -
8, and 10. In
particular, connection 34 evenly distributes the contact stress between a head-
engaging
surface 42 (Fig. 8) of lip 24 and a lip-engaging surface 40 underneath a head
44 of a fastener
46, wherein fastener 46 connects lip 24 to a lip-hinge member 48, which, in
tum, helps
pivotally connect lip 24 to deck 16.
Figures 9 and 10 show a comparison of the contact stress areas of the old and
new designs respectively. For the dock leveler of the '598 patent, Figure 9
shows a shaded
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crosshatched stress area 45 where the head of the fastener engages the lip.
For the new
design, Figure 10 shows that dock leveler 14 has a more broadly distributed
contact stress
area 47, which greatly enhances the longevity of the crown defining angle 38
and reduces the
fatigue of the material of the head engaging surface 24.
Although the actual hinge structure for connecting lip 24 to deck 16 may vary,
in some embodiments, hinge 22 comprises a hinge pin 50 that pivotally joins a
series of
spools or deck-hinge members 52 to the series of lip-hinge members 48. Deck-
hinge
members 52 are disposed about pin 50 and can be welded (depicted by numeral
54) or
otherwise attached to a header 56 of deck 16. Lip-hinge members 48 also
include spools 58
disposed about pin 50, whereby pin 50 pivotally connects spools 58 of the lip-
hinge members
48 to the series of deck-hinge members 52.
To create sliding connection 34, lip 24 includes a series of slots 60 along
which fasteners 46 can slide. In some embodiments, fastener 46 is a shoulder
screw that
includes head 44 and a shank 62. A threaded end of shank 62 screws into lip-
hinge member
48, and head 44, and an upper portion of shank 62 slides within slot 60. To
ensure sliding
clearance between lip 24 and a lip-facing surface 64 of lip-hinge member 48, a
gap 66 may
exist between the two. Gap 66 defines an acute angle 68 when lip 24 and lip-
hinge member
48 are in the extended operative position as shown in Figures 5 and 8.
To evenly distribute the circumferential contact stress between head 44 and
lip
24 when lip 24 is in its extended operative position of Figure 3, lip-engaging
surface 40 of
head 44 lies squarely on the integral head-engaging surface 42 of slot 60, as
shown in Figure
8. This is accomplished by having a longitudinal centerline 70 of fastener 46
be tilted out of
perpendicularity with lip-facing surface 64 and by having lip-engaging surface
40 of head 44
be perpendicular to centerline 70. So that lip-engaging surface 40 is
substantially coplanar
with head-engaging surface 42, the amount of tilt (i.e., an angle 73) between
centerline 70
and a line 75 perpendicular to surface 64 is substantially equal to acute
angle 68. Since lip-
engaging surface 40 is parallel with head-engaging surface 42, a head-to-hinge
angle 72 is
created between lip-engaging surface 40 and lip-facing surface 64, wherein the
head-to-hinge
angle 72 substantially equals acute angle 68.
In another embodiment, shown in Figures 11 -13 (which correspond to
Figures 5 - 7 respectively), a lip-hinge member 74 replaces lip-hinge member
48, and a deck-
hinge member 76 replaces deck-hinge member 52. Deck-hinge member 76 is a
formed metal
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plate that partially wraps around hinge pin 50 and is welded to a series of
deck-support beams
78 or otherwise attached to a deck 80. Deck-hinge member 76 has a series of
openings 82
through which lip-hinge members 74 extend. In this example, each lip-hinge
member 74
comprises a U-shaped piece 84, an upper plate 86, and a lower plate 88. U-
shaped piece 84
extends from upper plate 86 and wraps partially around hinge pin 50 so that
pin 50 pivotally
couples lip-hinge member 74 to deck-hinge member 76. Lower plate 88 underneath
upper
plate 86 provides a threaded hole for holding fastener 46.
To ensure sliding clearance between lip 24 and a lip-facing surface 90 of lip-
hinge member 86, a gap 94 may exist between the two. Gap 94 defines an acute
angle 92
when lip 24 and lip-hinge member 86 are positioned in the extended operative
position as
shown in Figure 11.
To evenly distribute the circumferential contact stress between head 44 and
lip
24 when lip 24 is in its extended operative position, lip-engaging surface 40
of head 44 lies
squarely on the integral head-engaging surface 42 of slot 60, as shown in
Figure 11. This is
accomplished by having centerline 70 of fastener 46 be tilted out of
perpendicularity with lip-
facing surface 90 and by having lip-engaging surface 40 of head 44 be
perpendicular to
centerline 70. The amount of tilt is substantially equal to acute angle 92 so
that lip-engaging
surface 40 is substantially coplanar with head-engaging surface 42.
Although the invention is described with reference to a preferred embodiment,
it should be appreciated by those of ordinary skill in the art that various
modifications are
well within the scope of the invention. A annular shim or conventional washer,
for instance,
could be placed underneath the head of the fastener, in which case the
fastener would
comprises the head, shank and washer (or shim), and the washer or shim would
be considered
as being part of the head. Therefore, the scope of the invention is to be
determined by
reference to the following claims:
